When you need a quick summary of the essentials, rather than the whole story or a thorough explanation, you're looking for the gist.
The word gist has had a variety of meanings in English, but most of them have become obsolete. The surviving sense of the word entered the language by way of the law: The gist of any legal action is the factor on which the action depends — that is, an alleged assault might be the gist of an indictment. The meaning of gist has evolved, though, and now it can be used to describe the core component of any matter, as in, "He watched the trailer, but he still didn't get the gist of the movie." Or, "She was having trouble writing a headline that conveyed the gist of her article."